The present invention relates to composite wheel rims, and more particularly, to a reinforced composite rim for use on human-powered vehicles, such as bicycles and wheelchairs.
Carbon fiber rims (also more broadly referred to herein as fiber resin plastic rims and composite rims) are strong and lightweight, making them popular for use in human-powered vehicle wheels. A carbon fiber composite rim is made up of sheets of material, similar to sheets of fabric. These sheets comprise carbon fibers that are cured within a bed of epoxy. The fibers within the bed of epoxy may be oriented in a desired direction For example, the carbon fibers may be oriented in a North-to-South direction, or alternatively, in an East-to-West direction. Although carbon fibers are very strong in their direction of orientation, they are less strong in directions perpendicular thereto.
One disadvantage of carbon fiber rims is that they are typically not well suited to absorb impacts in a radial direction, a type of impact that may occur when a bicycle wheel hits a pothole. In a hard pothole hit, a radially-outwardly-facing, tire-engaging surface of the wheel may strike an edge of the pothole, possibly causing a conventional rim to delaminate or develop cracks.
Looking to FIG. 1, a prior art wheel rim 170 is shown. The prior art rim 170 includes a first sidewall portion 172 and a second sidewall portion 174. The sidewall portions 172, 174 extend between a radially inner portion 176 of the rim and a radially outer portion 177 that includes a radially outwardly-facing, tire-engaging surface 178. The tire-engaging surface 178 is circumferential, generally forming the radially outermost portion of the rim. A plurality of spokes 189 extend radially between the radially inner portion 176 of the rim 170 and a hub (not shown) disposed at the axle of the wheel.
The configuration of the radially outwardly-facing surface of a bicycle wheel will vary depending on whether the wheel includes a “sew-up” rim or a “clincher” rim. In “sew-up” rims, a tire is glued to the tire-engaging surface 178. The rim in FIG. 1 has a “sew-up” configuration.
A clincher rim, on the other hand, includes a pair of generally upstanding members that include axially inwardly-extending beads configured to matingly engage the beads of a tire, the tire receiving a tube therein. The rim in FIG. 4 has a “clincher” configuration.
The rim 170 is a sew-up type rim. The tire-engaging surface 178 includes a first crown portion 180 and a second crown portion 182. Between the crown portions or “tows” 180, 182 is a valley 186.
When a tire and rim hit a pothole, the peaks of the crowns 180, 182 are the portions of the rim 170 most likely to strike the edge of a pothole and receive the full impact of the radial impact forces. For this reason, the two crown sections 180, 182 of the rim are the regions most susceptible to damage.
To reinforce the crown portions 180, 182, carbon fiber reinforcers or fiber bundles 184, 188 extend circumferentially about the rim. These fiber reinforcement bundles 184, 188 may comprise a plurality of carbon fibers, typically including about 48,000 very thin fibers.
The reinforcing bundles 184, 188 are sandwiched between layers of carbon fiber sheets of “fabric.” Typically, the outer portion 177 of the carbon fiber rim 170, that includes the tire-engaging portion 178, may include as few as four or five sheets of carbon fiber material, in addition to the reinforcing bundles 184, 188, or as many as 20 sheets; the more sheets of carbon fiber used, the greater the strength of the rim, however, at the expense of weight and cost.
Although the reinforcing bundles 184, 188 may improve the strength of the crowns 180, 182, the bundles and the composite sheets may shift laterally relative to each other. This “shifting” may also be described as ‘cleaving,’ splitting or ‘delaminating’. Although the carbon fiber reinforcer bundles 184, 188 help to reduce delamination, rims that include these reinforcer bundles 184, 188 are still subject to delamination.